Cooperation with digital frequency-translation repeater for uplink transmission and reception-ue behavior

ABSTRACT

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE generates R layers of baseband data signals to be carried on N2 subcarriers, where N2 and R are positive integers. The UE maps each of the R layers of baseband data signals to NT antennas in some or all of L first transmission time intervals using R precoders, with each precoder containing L·NT elements, and NT and L being positive integers. The UE transmits a first OFDM-based time-domain signal corresponding to the mapped baseband data signals across the L first transmission time intervals to a base station via one or more repeaters, where the L first transmission time intervals correspond to one second transmission time interval.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefits of U.S. Provisional ApplicationSer. No. 63/347,046, entitled “COOPERATION WITH DIGITALFREQUENCY-TRANSLATION REPEATER OVER DIFFERENT FR FOR UL TRANSMISSION-UEBEHAVIOR” and filed on May 31, 2022. The content of the applicationabove is expressly incorporated by reference herein in its entirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, andmore particularly, to techniques of forming distributed MIMO receivers.

Background

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. Some aspects of 5G NR may be based on the 4G Long TermEvolution (LTE) standard. There exists a need for further improvementsin 5G NR technology. These improvements may also be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. The apparatus may be a UE. The UEgenerates R layers of baseband data signals to be carried on N₂subcarriers, where N₂ and R are positive integers. The UE maps each ofthe R layers of baseband data signals to N_(T) antennas in some or allof L first transmission time intervals using R precoders, with eachprecoder containing L·N_(T) elements, and N_(T) and L being positiveintegers. The UE transmits a first OFDM-based time-domain signalcorresponding to the mapped baseband data signals across the L firsttransmission time intervals to a base station via one or more repeaters,where the L first transmission time intervals correspond to one secondtransmission time interval.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIG. 2 is a diagram illustrating a base station in communication with aUE in an access network.

FIG. 3 illustrates an example logical architecture of a distributedaccess network.

FIG. 4 illustrates an example physical architecture of a distributedaccess network.

FIG. 5 is a diagram showing an example of a DL-centric slot.

FIG. 6 is a diagram showing an example of an UL-centric slot.

FIG. 7 is a diagram illustrating uplink MIMO transmission from a UE to abase station via one or more repeaters.

FIG. 8 is a diagram illustrating RF signal generation at a UE.

FIG. 9 is a diagram illustrating uplink transmission timing from a UE toa base station via one or more repeaters.

FIG. 10 is a diagram illustrating uplink transmission according to anon-coherent joint transmission (NCJT) approach.

FIG. 11 is a diagram illustrating uplink transmission according to acoherent joint transmission (CJT) approach.

FIG. 12 is a diagram illustrating signal transformation at a repeater.

FIG. 13 is a diagram illustrating signal reception at a base station.

FIG. 14 is a diagram illustrating a method (process) for uplinkcommunications.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunications systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example aspects, the functions described maybe implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, an Evolved Packet Core (EPC) 160, and anothercore network 190 (e.g., a 5G Core (5GC)). The base stations 102 mayinclude macrocells (high power cellular base station) and/or small cells(low power cellular base station). The macrocells include base stations.The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to asEvolved Universal Mobile Telecommunications System (UMTS) TerrestrialRadio Access Network (E-UTRAN)) may interface with the EPC 160 throughbackhaul links 132 (e.g., SI interface). The base stations 102configured for 5G NR (collectively referred to as Next Generation RAN(NG-RAN)) may interface with core network 190 through backhaul links184. In addition to other functions, the base stations 102 may performone or more of the following functions: transfer of user data, radiochannel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160 or corenetwork 190) with each other over backhaul links 134 (e.g., X2interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacrocells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to X MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz)bandwidth per carrier allocated in a carrier aggregation of up to atotal of Yx MHz (x component carriers) used for transmission in eachdirection. The carriers may or may not be adjacent to each other.Allocation of carriers may be asymmetric with respect to DL and UL(e.g., more or fewer carriers may be allocated for DL than for UL). Thecomponent carriers may include a primary component carrier and one ormore secondary component carriers. A primary component carrier may bereferred to as a primary cell (PCell) and a secondary component carriermay be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 158. The D2D communication link 158 may use theDL/UL WWAN spectrum. The D2D communication link 158 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available. The small cell 102′may operate in a licensed and/or an unlicensed frequency spectrum. Whenoperating in an unlicensed frequency spectrum, the small cell 102′ mayemploy NR and use the same 5 GHz unlicensed frequency spectrum as usedby the Wi-Fi AP 150. The small cell 102′, employing NR in an unlicensedfrequency spectrum, may boost coverage to and/or increase capacity ofthe access network.

A base station 102, whether a small cell 102′ or a large cell (e.g.,macro base station), may include an eNB, gNodeB (gNB), or another typeof base station. Some base stations, such as gNB 180 may operate in atraditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies,and/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band (e.g., 3 GHz-300 GHz) hasextremely high path loss and a short range. The mmW base station 180 mayutilize beamforming 182 with the UE 104 to compensate for the extremelyhigh path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 inone or more transmit directions 108 a. The UE 104 may receive thebeamformed signal from the base station 180 in one or more receivedirections 108 b. The UE 104 may also transmit a beamformed signal tothe base station 180 in one or more transmit directions. The basestation 180 may receive the beamformed signal from the UE 104 in one ormore receive directions. The base station 180/UE 104 may perform beamtraining to determine the best receive and transmit directions for eachof the base station 180/UE 104. The transmit and receive directions forthe base station 180 may or may not be the same. The transmit andreceive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The core network 190 may include a Access and Mobility ManagementFunction (AMF) 192, other AMFs 193, a location management function (LMF)198, a Session Management Function (SMF) 194, and a User Plane Function(UPF) 195. The AMF 192 may be in communication with a Unified DataManagement (UDM) 196. The AMF 192 is the control node that processes thesignaling between the UEs 104 and the core network 190. Generally, theSMF 194 provides QoS flow and session management. All user Internetprotocol (IP) packets are transferred through the UPF 195. The UPF 195provides UE IP address allocation as well as other functions. The UPF195 is connected to the IP Services 197. The IP Services 197 may includethe Internet, an intranet, an IP Multimedia Subsystem (IMS), a PSStreaming Service, and/or other IP services.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), a transmit reception point(TRP), or some other suitable terminology. The base station 102 providesan access point to the EPC 160 or core network 190 for a UE 104.Examples of UEs 104 include a cellular phone, a smart phone, a sessioninitiation protocol (SIP) phone, a laptop, a personal digital assistant(PDA), a satellite radio, a global positioning system, a multimediadevice, a video device, a digital audio player (e.g., MP3 player), acamera, a game console, a tablet, a smart device, a wearable device, avehicle, an electric meter, a gas pump, a large or small kitchenappliance, a healthcare device, an implant, a sensor/actuator, adisplay, or any other similar functioning device. Some of the UEs 104may be referred to as IoT devices (e.g., parking meter, gas pump,toaster, vehicles, heart monitor, etc.). The UE 104 may also be referredto as a station, a mobile station, a subscriber station, a mobile unit,a subscriber unit, a wireless unit, a remote unit, a mobile device, awireless device, a wireless communications device, a remote device, amobile subscriber station, an access terminal, a mobile terminal, awireless terminal, a remote terminal, a handset, a user agent, a mobileclient, a client, or some other suitable terminology.

Although the present disclosure may reference 5G New Radio (NR), thepresent disclosure may be applicable to other similar areas, such asLTE, LTE-Advanced (LTE-A), Code Division Multiple Access (CDMA), GlobalSystem for Mobile communications (GSM), or other wireless/radio accesstechnologies.

FIG. 2 is a block diagram of a base station 210 in communication with aUE 250 in an access network. In the DL, IP packets from the EPC 160 maybe provided to a controller/processor 275. The controller/processor 275implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 275provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 216 and the receive (RX) processor 270implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 216 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 274 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 250. Each spatial stream may then be provided to a differentantenna 220 via a separate transmitter 218TX. Each transmitter 218TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 250, each receiver 254RX receives a signal through itsrespective antenna 252. Each receiver 254RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 256. The TX processor 268 and the RX processor 256implement layer 1 functionality associated with various signalprocessing functions. The RX processor 256 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 250. If multiple spatial streams are destined for the UE 250,they may be combined by the RX processor 256 into a single OFDM symbolstream. The RX processor 256 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 210. These soft decisions may be based on channelestimates computed by the channel estimator 258. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 210 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 259, which implements layer 3 and layer 2functionality. The controller/processor 259 can be associated with amemory 260 that stores program codes and data. The memory 260 may bereferred to as a computer-readable medium. In the UL, thecontroller/processor 259 provides demultiplexing between transport andlogical channels, packet reassembly, deciphering, header decompression,and control signal processing to recover IP packets from the EPC 160.The controller/processor 259 is also responsible for error detectionusing an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 210, the controller/processor 259provides RRC layer functionality associated with system information(e.g., MIB, SIBs) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 258 from a referencesignal or feedback transmitted by the base station 210 may be used bythe TX processor 268 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 268 may be provided to different antenna252 via separate transmitters 254TX. Each transmitter 254TX may modulatean RF carrier with a respective spatial stream for transmission. The ULtransmission is processed at the base station 210 in a manner similar tothat described in connection with the receiver function at the UE 250.Each receiver 218RX receives a signal through its respective antenna220. Each receiver 218RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 270.

The controller/processor 275 can be associated with a memory 276 thatstores program codes and data. The memory 276 may be referred to as acomputer-readable medium. In the UL, the controller/processor 275provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 250. IP packets from thecontroller/processor 275 may be provided to the EPC 160. Thecontroller/processor 275 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

New radio (NR) may refer to radios configured to operate according to anew air interface (e.g., other than Orthogonal Frequency DivisionalMultiple Access (OFDMA)-based air interfaces) or fixed transport layer(e.g., other than Internet Protocol (IP)). NR may utilize OFDM with acyclic prefix (CP) on the uplink and downlink and may include supportfor half-duplex operation using time division duplexing (TDD). NR mayinclude Enhanced Mobile Broadband (eMBB) service targeting widebandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting highcarrier frequency (e.g. 60 GHz), massive MTC (mMTC) targetingnon-backward compatible MTC techniques, and/or mission criticaltargeting ultra-reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHz may be supported. In oneexample, NR resource blocks (RBs) may span 12 sub-carriers with asub-carrier bandwidth of 60 kHz over a 0.25 ms duration or a bandwidthof 30 kHz over a 0.5 ms duration (similarly, 50 MHz BW for 15 kHz SCSover a 1 ms duration). Each radio frame may consist of 10 subframes (10,20, 40 or 80 NR slots) with a length of 10 ms. Each slot may indicate alink direction (i.e., DL or UL) for data transmission and the linkdirection for each slot may be dynamically switched. Each slot mayinclude DL/UL data as well as DL/UL control data. UL and DL slots for NRmay be as described in more detail below with respect to FIGS. 5 and 6 .

The NR RAN may include a central unit (CU) and distributed units (DUs).A NR BS (e.g., gNB, 5G Node B, Node B, transmission reception point(TRP), access point (AP)) may correspond to one or multiple BSs. NRcells can be configured as access cells (ACells) or data only cells(DCells). For example, the RAN (e.g., a central unit or distributedunit) can configure the cells. DCells may be cells used for carrieraggregation or dual connectivity and may not be used for initial access,cell selection/reselection, or handover. In some cases DCells may nottransmit synchronization signals (SS) in some cases DCells may transmitSS. NR BSs may transmit downlink signals to UEs indicating the celltype. Based on the cell type indication, the UE may communicate with theNR BS. For example, the UE may determine NR BSs to consider for cellselection, access, handover, and/or measurement based on the indicatedcell type.

FIG. 3 illustrates an example logical architecture of a distributed RAN300, according to aspects of the present disclosure. A 5G access node306 may include an access node controller (ANC) 302. The ANC may be acentral unit (CU) of the distributed RAN. The backhaul interface to thenext generation core network (NG-CN) 304 may terminate at the ANC. Thebackhaul interface to neighboring next generation access nodes (NG-ANs)310 may terminate at the ANC. The ANC may include one or more TRPs 308(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, orsome other term). As described above, a TRP may be used interchangeablywith “cell.”

The TRPs 308 may be a distributed unit (DU). The TRPs may be connectedto one ANC (ANC 302) or more than one ANC (not illustrated). Forexample, for RAN sharing, radio as a service (RaaS), and servicespecific ANC deployments, the TRP may be connected to more than one ANC.A TRP may include one or more antenna ports. The TRPs may be configuredto individually (e.g., dynamic selection) or jointly (e.g., jointtransmission) serve traffic to a UE.

The local architecture of the distributed RAN 300 may be used toillustrate fronthaul definition. The architecture may be defined thatsupport fronthauling solutions across different deployment types. Forexample, the architecture may be based on transmit network capabilities(e.g., bandwidth, latency, and/or jitter). The architecture may sharefeatures and/or components with LTE. According to aspects, the nextgeneration AN (NG-AN) 310 may support dual connectivity with NR. TheNG-AN may share a common fronthaul for LTE and NR.

The architecture may enable cooperation between and among TRPs 308. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 302. According to aspects, no inter-TRP interface may beneeded/present. According to aspects, a dynamic configuration of splitlogical functions may be present within the architecture of thedistributed RAN 300. The PDCP, RLC, MAC protocol may be adaptably placedat the ANC or TRP.

FIG. 4 illustrates an example physical architecture of a distributed RAN400, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 402 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.A centralized RAN unit (C-RU) 404 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge. A distributed unit (DU) 406 may host one or more TRPs. The DU maybe located at edges of the network with radio frequency (RF)functionality.

FIG. 5 is a diagram 500 showing an example of a DL-centric slot. TheDL-centric slot may include a control portion 502. The control portion502 may exist in the initial or beginning portion of the DL-centricslot. The control portion 502 may include various scheduling informationand/or control information corresponding to various portions of theDL-centric slot. In some configurations, the control portion 502 may bea physical DL control channel (PDCCH), as indicated in FIG. 5 . TheDL-centric slot may also include a DL data portion 504. The DL dataportion 504 may sometimes be referred to as the payload of theDL-centric slot. The DL data portion 504 may include the communicationresources utilized to communicate DL data from the scheduling entity(e.g., UE or BS) to the subordinate entity (e.g., UE). In someconfigurations, the DL data portion 504 may be a physical DL sharedchannel (PDSCH).

The DL-centric slot may also include a common UL portion 506. The commonUL portion 506 may sometimes be referred to as an UL burst, a common ULburst, and/or various other suitable terms. The common UL portion 506may include feedback information corresponding to various other portionsof the DL-centric slot. For example, the common UL portion 506 mayinclude feedback information corresponding to the control portion 502.Non-limiting examples of feedback information may include an ACK signal,a NACK signal, a HARQ indicator, and/or various other suitable types ofinformation. The common UL portion 506 may include additional oralternative information, such as information pertaining to random accesschannel (RACH) procedures, scheduling requests (SRs), and various othersuitable types of information.

As illustrated in FIG. 5 , the end of the DL data portion 504 may beseparated in time from the beginning of the common UL portion 506. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric slot and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 6 is a diagram 600 showing an example of an UL-centric slot. TheUL-centric slot may include a control portion 602. The control portion602 may exist in the initial or beginning portion of the UL-centricslot. The control portion 602 in FIG. 6 may be similar to the controlportion 502 described above with reference to FIG. 5 . The UL-centricslot may also include an UL data portion 604. The UL data portion 604may sometimes be referred to as the pay load of the UL-centric slot. TheUL portion may refer to the communication resources utilized tocommunicate UL data from the subordinate entity (e.g., UE) to thescheduling entity (e.g., UE or BS). In some configurations, the controlportion 602 may be a physical DL control channel (PDC CH).

As illustrated in FIG. 6 , the end of the control portion 602 may beseparated in time from the beginning of the UL data portion 604. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric slot may alsoinclude a common UL portion 606. The common UL portion 606 in FIG. 6 maybe similar to the common UL portion 506 described above with referenceto FIG. 5 . The common UL portion 606 may additionally or alternativelyinclude information pertaining to channel quality indicator (CQI),sounding reference signals (SRSs), and various other suitable types ofinformation. One of ordinary skill in the art will understand that theforegoing is merely one example of an UL-centric slot and alternativestructures having similar features may exist without necessarilydeviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

FIG. 7 is a diagram 700 illustrating uplink MIMO transmission from a UEto a base station via one or more repeaters. In this example, a UE 704has 2 transmission antennas 712-1, 712-2 and a base station 702 has 8antennas 710-1, 710-2, . . . 710-8. Further, repeaters 706-1 . . . 706-Kare placed between the base station 702 and the UE 704. In this example,K is 4. Each of the repeaters 706-1 . . . 706-K has two receptionantennas 722-1, 722-2 and two transmission antennas 724-1, 724-2. Incertain configurations, the same antenna may function as a receptionantenna and a transmission antenna.

The UE 704 utilizes a respective transmission chain 740 to generate RFsignals to be transmitted at transmission antennas 712-1, 712-2. Eachtransmission chain 740 includes an IFFT component 741, a parallel toserial component 742, a CP insertion component 743, a conversioncomponent 744 that includes a rate converter and/or filter(s), adigital-to-analog converter 745, and an up converter 746. FIG. 8 is adiagram 800 illustrating RF signal generation at a UE. In this example,the UE 704 may be configured with 2 antenna ports 850-1, 850-2 to eachof which one or more of the antennas 712-1, 712-2 are assigned. Inparticular, each of the antenna ports 850-1, 850-2 may be associatedwith more than one physical antenna. In such a case, each of the antennaport may be referred to as a beamformed antenna port. Further, eachtransmission chain 740 may use N₁ subcarriers 810 (e.g., 4096subcarriers) having a SCS₁ (e.g., 120 kHz). The transmission chain 740of the transmission antenna 712-i receives, from an i^(th) antenna port,a k^(th) group of N₁ modulation symbols 820-i, denoted as y_(k,i), andgenerates corresponding RF signals to be transmitted through thetransmission antenna 712-i in an OFDM symbol A, which corresponds toSCS₁. k is the group index of the modulation symbols and i is the indexof the antenna port.

Using the transmission antenna 712-1 as an example, that antenna isassigned to the antenna port 850-1. A k^(th) group of N₁ modulationsymbols 820-1 from the antenna port 850-1, y_(k,1), are to betransmitted in one OFDM symbol A through the transmission chain 740. TheUE 704 applies y_(k,1) to the N₁ subcarriers 810 in a corresponding timeperiod.

Referring back to FIG. 7 , the N₁ subcarriers 810 carrying the N₁modulation symbols 820-1 are sent to the IFFT component 741 with N₁inputs. The N₁ time domain signals output from the IFFT component 741are treated as a time sequence and sent to the parallel to serialcomponent 742 to form a combined time domain signal. The CP insertioncomponent 743 receives the combined time domain signal and adds a cyclicprefix, resulting a time domain signal spanning an OFDM symbol. Thecyclic prefix may eliminate inter-symbol interference between twoadjacent OFDM symbols. The resulting time domain signal is in digitalform, and processed through the conversion component 744 to achieve adesired sample rate. The converted time domain signal in digital form issent to the digital-to-analog converter 745, which accordingly generatesan analog time domain signal. Subsequently, the up converter 746receives the analog time domain signal and mixes the analog time domainsignal with a first carrier frequency (f₁) to generate a RF signal. TheRF signal is transmitted through the antenna 712-1 of the UE 704. Inparticular, the first carrier frequency of the RF signals transmittedfrom the UE 704 may be in FR2.

Similarly, the antenna ports 850-2 receives modulation symbols. Atransmission chain 740 assigned to the antenna ports 850-2 accordinglygenerates corresponding RF signals, which are transmitted through anantenna assigned to the antenna ports 850-2. As such, in this example,y_(k,1) and y_(k,2) are transmitted through the transmission antennas712-1 and 712-2.

FIG. 9 is a diagram 900 illustrating uplink transmission timing from aUE to a base station via one or more repeaters. The UE 704 transmits,through the transmission antennas 712-1 and 712-2, RF signals on a firstcarrier frequency in slots 910-0, . . . , 910-q, slots 911-0, . . . ,911-q, and slots 912-0, . . . , 912-q, etc. The slots 910-0, . . . ,910-q, etc. are corresponding to a first subcarrier spacing (SCS₁, e.g.,120 kHz). As described infra, the slots 920-0, . . . , 920-q, slots921-0, . . . , 921-q, and slots 922-0, . . . , 922-q, etc. arecorresponding to the first subcarrier spacing (SCS₁). The repeaters706-1 . . . 706-K receive the RF signals of the first carrier frequencyin the slots 920-0, . . . , 920-q, slots 921-0, . . . , 921-q, and slots922-0, . . . , 922-q, etc. The repeaters 706-1 . . . 706-K transform afirst set of baseband signals carried on the RF signals of the firstcarrier frequency to obtain a second set of baseband signals, andtransmit the second set of baseband signals over RF signals of a secondcarrier frequency in slots 930-0, 930-1, 930-2, etc. As described infra,the slots 930-0, 930-1, 930-2, etc. are corresponding to a secondsubcarrier spacing (SCS₂, e.g., 30 kHz). The base station 702 receivesthe RF signals of the second carrier frequency in slots 940-0, 940-1,940-2, etc. The slots 940-0, 940-1, 940-2, etc. are corresponding to thesecond subcarrier spacing (SCS₂). In this example, q is 3. In NR, a slotmay be an interval occupied by 14 OFDM symbols. The repeaters receivesignal at the first frequency in the high frequency band, which may notbe able to be used for direct transmission to the base station due tolimited coverage. After repeater operations, the signal is forwarded bythe repeaters at the second frequency in the low frequency band, whichprovides much wider coverage for the base station. As a result, we cantrade the un-used/out-of-coverage bandwidth in the high frequency bandfor additional spatial multiplexing gain in the low frequency band.

The time duration of each of the slots 920-0, . . . , 920-q, etc. isTTI₁. The time duration of each of the slots 930-0, 930-1, 930-2, etc.is TTI₂. Denote L=SCS₁/SCS₂=TTI₂/TTI₁. Denote the first carrierfrequency as and the second carrier frequency as f₂.

The UE 704 transmits the RF signals on f₁ to the k^(th) repeater att₀×TTI₂+(k−1)×TTI1(k=1, . . . , K) (e.g., slots 910-0, . . . , 910-q),t₀ is the time index defined according to TTI₂. In this example, the UE704 transmits the RF signals to the repeater 706-1 in slot 910-0, to therepeater 706-2 in slot 910-1, to the repeater 706-3 in slot 910-2 and tothe repeater 706-4 in slot 910-3.

Each of the repeaters 706-1 . . . 706-K receives and transmitsrespective RF signals of f₁ as described infra. The k^(th) repeaterreceives its RF signals of f₁ in t₀×TTI₂+(k−1)×TTI1(k=1, . . . , K) andtransmits the RF signals of f₂ in (t₀+offset)×TTI₂. The offset (e.g., 1)is set to provide sufficient time for signal receiving and processing ata repeater. The number of repeaters 706-1 . . . 706-K (i.e., K) is atmost L where is SCS₁/SCS₂=TTI₂/TTI₁, to utilize the full timing resourcefor transmission. In this example, the repeater 706-1 receives the RFsignals in slots 920-0 and waits 3 slots (i.e., 920-1, 920-2, 920-3),the repeater 706-2 receives the RF signals in slots 920-1 and waits 2slots (i.e., 920-2, 920-3), the repeater 706-3 receives the RF signalsin slots 920-2 and waits 1 slot (i.e., 920-3), the repeater 706-4receives the RF signals in slots 920-3. The repeaters 706-1, 706-2,706-3 and 706-4 transmit their own RF signals to the base station 702simultaneously in the next TTI₂ slot 930-0.

Referring back to FIG. 7 , as described supra, there are K repeaters706-1 . . . 706-K placed between the base station 702 and the UE 704. Ingeneral, a repeater has M_(r) reception antennas and M_(t) transmissionantennas. In this example, for ease of presentation, M_(t)=M_(r)=M. Asingle physical antenna may function as both a reception antenna and atransmission antenna. More specifically, M is 2. Each of the repeaters706-1 . . . 706-K has reception antennas 722-1, 722-2 and transmissionantennas 724-1, 724-2.

Each of the repeaters 706-1 . . . 706-K receives RF signals transmittedfrom the UE 704. For example, each of the reception antennas 722-1,722-2 of the repeater 706-1 may receive RF signals transmitted from theantennas 712-1, 712-2 of the UE 704. A respective reception chain 750processes RF signals received through each of the reception antennas722-1, 722-2. The reception chain 750 includes a down converter 756, ananalog-to-digital converter 755, a conversion component 754 thatincludes a rate converter and/or filter(s), a CP removal component 753,a serial to parallel component 752, an FFT component 751.

Using the reception antenna 722-1 as an example, the corresponding downconverter 756 processes the RF signals received through that antenna toobtain corresponding analog baseband signals, for example, throughfrequency down-conversion. The analog-to-digital converter 755 convertsthe analog baseband signals to digital samples. In particular, togenerate the channel signal samples from a baseband waveform, thebaseband waveform may be sampled at a rate higher than its Nyquistsampling rate by the analog-to-digital converter 755.

The digital samples are then passed through the conversion component754, which contains one or more digital filters. The digital filters mayperform various functions including I-Q imbalance compensation, carriersynchronization, and/or timing synchronization, etc. to eliminate someimperfections in hardware.

FIG. 10 is a diagram 1000 illustrating uplink transmission according toa non-coherent joint transmission (NCJT) approach. Non-coherenttransmission here means that coherent transmission of a transmissionantenna across multiple TTI₁ intervals is not guaranteed. In thisexample, the base station 702 have 8 antennas corresponding 8 receptionantenna ports and the UE 704 has 2 antennas corresponding 2 receptionantenna ports. The repeaters 706-1, . . . , 706-K are placed between thebase station 702 and the UE 704.

In the NCJT configuration, the UE 704 transmits multiple layers ofbaseband signals across multiple TTI₁ intervals (i.e., slots 920-0, . .. , 920-3) corresponding to one TTI₂ interval (i.e., slot 930-0) to thebase station 702 through the repeaters 706-1, . . . , 706-K. In each ofthe multiple TTI₁ intervals, the UE 704 transmits some, but not all, ofthe multiple layers of baseband signals. The TTI₂ interval is subsequentto the corresponding TTI₁ intervals.

In this example, the UE 704 generates 8 layers baseband data signalsx_(1,n), x_(2,n), . . . x_(8,n) (or modulation symbols) on a subcarriern, which can be represented by a vector:

$x_{n_{8 \times 1}} = {\begin{bmatrix}\begin{matrix}\begin{matrix}x_{1,n} \\x_{2,n}\end{matrix} \\ \vdots \end{matrix} \\x_{8,n}\end{bmatrix}.}$

The UE 704 divides the symbols x_(n) _(8×1) into 4 layer groups x₁_(2×1) , x₂ _(2×1) , x₃ _(2×1) and x₄ _(2×1) , each corresponding to oneof the 4 TTI₁ intervals:

${x_{1,n_{2 \times 1}} = \begin{bmatrix}x_{1,n} \\x_{2,n}\end{bmatrix}};{x_{2,n_{2 \times 1}} = \begin{bmatrix}x_{3,n} \\x_{4,n}\end{bmatrix}};{x_{3,n_{2 \times 1}} = \begin{bmatrix}x_{5,n} \\x_{6,n}\end{bmatrix}};{x_{4,n_{2 \times 1}} = {\begin{bmatrix}x_{7,n} \\x_{8,n}\end{bmatrix}.}}$

During one TTI₁ interval, the UE 704 transmits baseband signals of oneof the 4 layer groups, using a precoder to map the baseband signals ofthe corresponding layer group to the antennas of the UE 704. In eachTTI₁ interval, the UE transmits signals by two antennas. Considering the4 TTI₁ intervals together, the UE appears to be transmitting signals by8 effective antennas, and the corresponding 8-by-1 precoder to beapplied on the 8 effective antennas for each layer contains at most twonon-zero elements corresponding to one of the four TTI₁ intervals. Notethe 8-by-1 precoder can be equivalently expressed by four 2-by-1precoders separately used in the 4 TTIs. This process ensures that thebaseband signals are transmitted efficiently and effectively to the basestation 702 through the repeaters 706-1 . . . 706-K.

In this example, more specifically, the UE 704 uses a precoder P_(1,n)_(2×2) to map the baseband data signals x_(1,n) _(2×1) on the subcarriern to the 2 transmission antennas to generate 2 baseband signals y_(1,n)_(2×1) in the slot 910-0, which can be represented as y_(1,n) _(2×1)=P_(1,n) _(2×2) ·x_(1,n) _(2×1) . Further, the UE 704 mixes y_(1,n)_(2×1) with RF carriers of f₁ to generate 2 RF signals and transmits theRF signals to the repeater 706-1 in slot 910-0 through a channel 1010which can be represented as H_(1,n) _(2×2) ⁽¹⁾.

The repeater 706-1 receives, in the slot 920-0, the RF signalstransmitted from the UE 704. The impact, of the rate conversion andfrequency translation (RCFT) process, to the base band signals can berepresented as T₁. The repeater 706-1 further transmits the RF signalsof f₂, generated through the RCFT process, to the base station 702 inthe slot 930-0 through a channel 1030 which can be represented asH_(1,n) _(8×2) ⁽²⁾. Accordingly, on the subcarrier n, the basebandsignals received by the base station 702 from the repeater 706-1 can berepresented as

r _(1,n) _(8×1) =H _(1,n) _(8×2) ⁽²⁾ ·T ₁ ·H _(1,n) _(2×2) ⁽¹⁾ ·P _(1,n)_(2×2) ·x _(1,n) _(2×1) +n ₁ =H _(1,n) _(8×2) ⁽²⁾ ·T ₁ ·H _(1,n) _(2×2)⁽¹⁾ ·y _(1,n) _(2×1) n ₁

n₁ is equivalent noise vector at the base station 702 which may containthe noise received at the repeater 706-1 and the base station 702.

Similarly, the repeaters 706-2, 706-3, 706-4 receive y_(2,n) _(2×1) ,y_(3,n) _(2×1) , y_(4,n) _(2×1) transmitted from the UE 704 on f₁ in theslots 920-1, 920-2, 920-3, respectively. The repeaters 706-2, 706-3,706-4 process the received RF signals through the RCFT processes andtransmit the result RF signals on f₂ in the slot 930-0. The base station702 receives the RF signals on f₂ transmitted from the repeaters 706-1 .. . 706-4 in the slot 940-0. The received baseband signal r_(n) _(8×1)at the base station 702 can be expressed as the sum of all signalsreceived from the repeaters 706-1, . . . , 706-4 as follows:

$\begin{matrix}{r_{n_{8 \times 1}} = {r_{1,n_{8 \times 1}} + r_{2,n_{8 \times 1}} + r_{3,n_{8 \times 1}} + r_{4,n_{8 \times 1}}}} \\{= {{H_{1,n_{8 \times 2}}^{(2)} \cdot T_{1} \cdot H_{1,n_{2 \times 2}}^{(1)} \cdot P_{1,n_{2 \times 2}} \cdot x_{1,n_{2 \times 1}}} + n_{1}}} \\{= {{{+ H_{2,n_{8 \times 2}}^{(2)}} \cdot T_{2} \cdot H_{2,n_{2 \times 2}}^{(1)} \cdot P_{2,n_{2 \times 2}} \cdot x_{2,n_{2 \times 1}}} + n_{2}}} \\{= {{{+ H_{3,n_{8 \times 2}}^{(2)}} \cdot T_{3} \cdot H_{3,n_{2 \times 2}}^{(1)} \cdot P_{3,n_{2 \times 2}} \cdot x_{3,n_{2 \times 1}}} + n_{3}}} \\{= {{{+ H_{4,n_{8 \times 2}}^{(2)}} \cdot T_{4} \cdot H_{4,n_{2 \times 2}}^{(1)} \cdot P_{4,n_{2 \times 2}} \cdot x_{4,n_{2 \times 1}}} + n_{4}}} \\{= {{\sum\limits_{\lbrack{= 1}}^{4}{H_{\lbrack{,n_{8 \times 2}}}^{(2)}\cdot T_{\lbrack}\cdot H_{\lbrack{,n_{2 \times 2}}}^{(1)}\cdot y_{\lbrack{,n_{2 \times 1}}}}} + n}} \\{= {{H_{{eq},n} \cdot \begin{bmatrix}y_{l,1,n} \\\ldots \\y_{l,8,n}\end{bmatrix}} + n}}\end{matrix}.$

H_(eq,n) is an equivalent channel matrix for the n-th subcarrier at thebase station 702, which is given by

H _(eq,n) =[H _(1,n) ⁽²⁾ ·T ₁ ·H _(1,n) ⁽¹⁾ , . . . ,H _(4,n) ⁽²⁾ ·T ₄·H _(4,n) ⁽¹⁾].

The base station 702 can decode the received baseband signal r_(n)_(8×1) based on the equivalent channel matrix H_(eq,n) and the precodingmatrices P_(1,n), P_(2,n), P_(3,n), and P_(4,n). By doing so, the basestation 702 can recover the transmitted baseband data signals x_(1,n). .. x_(4,n) (i.e., x_(1,n),x_(2,n), . . . , x_(8,n)) and maintain thedesired data transmission rate effectively.

Generally, the UE 704 has N_(T) transmission antennas, the base station702 has N_(R) reception antennas and the L repeaters 706-1, , 706-L withM_(T) transmission antennas and M_(R) reception antennas whereM_(T)=M_(R)=M are located between the UE 704 and the base station 702.The UE 704 may generate R layers baseband data signals. The UE 704divides the R layers baseband data signals into L groups and each grouphas R_(l) layers. The received baseband signal r_(n)∈

^(N) ^(R) ^(×1) at the n-th subcarrier at the base station 702 is thesum of signal transmitted from L repeaters 706-1, . . . , 706-L and itcan be expressed as below Equation (A):

$r_{n} = {{{{\sum}_{l = 1}^{L}H_{l,n}^{(2)}T_{l,n}{H_{l,n}^{(1)} \cdot P_{l,n} \cdot x_{l,n}}} + n_{n}} = {{{\sum}_{l = 1}^{L}H_{l,n}^{(2)}T_{l,n}{H_{l,n}^{(1)} \cdot \begin{bmatrix}y_{l,1,n} \\\ldots \\y_{l,N_{T},n}\end{bmatrix}}} + n_{n}}}$

where H_(l,n) ⁽²⁾∈

^(N) ^(R) ^(×M) denotes the channel matrix in the second hop from thel-th reapeater 706-1 to the base station 702, H_(l,n) ⁽¹⁾∈

^(M×N) ^(T) denotes the channel matrix in the first hop from the UE 704to the l-th reapeater 706-1, T_(l,n)∈

^(M×M) is an amplifying matrix describing the mapping from the repeaterinput to the repeater output, n_(n) is the equivalent noise vector atthe base station 702 which may contain the noise received at therepeaters 706-1, . . . , 706-L and the base station 702, x_(l,n)∈

^(R) ^(l) ^(×1) denote the rank-R_(l) signal transmitted by the UE overthe l-th TTI₁ interval, P_(l,n)∈

^(N) ^(T) ^(×R) ^(l) represent the precoding matrix of x_(l,n) for thel-th spatial transmitting setting and y_(l,i,n) denotes thefrequency-domain baseband signal at the n-th subcarrier for the i-th Txantenna. In a period of L TTI₁ intervals, the UE 704 may be consideredas having L·N_(T) effective antennas; however, not all of the effectiveantennas are guaranteed for supporting coherent transmission of aspatial layer in the NCJT configuration. Since number of data layers canbe transmitted is limited by number of Tx antennas of the UE, the UE 704can transmit at most N_(T) spatial layers in one TTI₁ interval. Hence,the total number of spatial layers in one TTI₂ interval is R=Σ_(l=1)^(L)R_(l), where R_(l)≤N_(T) for l=1, . . . , L.

Based on the equation, the base station 702 can determine R layersbaseband data signals x_(1,n), x_(2,n), . . . , x_(R,n) at the n-thsubcarrier. In this example, N_(R)=8, N_(T)=2, M_(R)=M_(T)=M=2, R=8, L=4and R_(l)=2 for l=1, . . . , L.

FIG. 11 is a diagram 1100 illustrating uplink transmission according toa coherent joint transmission (CJT) approach. Coherent transmission heremeans that coherent transmission of a transmission antenna acrossmultiple TTIi intervals is guaranteed. In this example, the base station702 have 8 antennas corresponding 8 reception antenna ports and the UE704 has 2 antennas corresponding 2 transmission antenna ports. Therepeaters 706-1, . . . , 706-K are placed between the base station 702and the UE 704.

In the CJT configuration, the UE 704 transmits all of the multiplelayers of baseband signals across each of multiple TTI₁ intervals (i.e.,slots 920-0, . . . , 920-3) corresponding to one TTI₂ interval (i.e.,slot 930-0) to the base station 702 through the repeaters 706-1, . . . ,706-K. The TTI₂ interval is subsequent to the corresponding TTI₁intervals. In each TTI₁ interval, the UE 704 transmits signals by twoantennas. Considering the 4 TTI₁ intervals together, the UE 704 appearsto be transmitting signals by 8 effective antennas. For the CJTconfiguration, the UE 704 should ensure coherent transmissions acrossthe 4 TTI₁ intervals. In other words, one layer of baseband data signalcan be coherently (or partially coherent) transmitted by the 8 effectivetransmission antennas.

In this example, the UE 704 generates 8 layers baseband data signalsx_(1,n), x_(2,n), . . . , x_(8,n) (or modulation symbols) on asubcarrier n, which can be represented by a vector:

$x_{n_{8 \times 1}} = {\begin{bmatrix}x_{1,n} \\x_{2,n} \\ \vdots \\x_{8,n}\end{bmatrix}.}$

During one TTI₁ interval, the UE 704 transmits baseband signals of x_(n)_(8×1) , using a precoder to map the baseband signals of thecorresponding layer group to the antennas of the UE 704. This processensures that the baseband signals are transmitted efficiently andeffectively to the base station 702 through the repeaters 706-1 . . .706-K.

In this example, more specifically, the UE 704 uses a precoder P_(1,n)_(2×8) to map the baseband data signals x_(n) _(8×1) on the subcarrier nto the 2 transmission antennas to generate 2 baseband signals y_(1,n)_(2×1) in the slot 910-0, which can be represented as y_(1,n) _(2×1)=P_(1,n) _(2×8) ·x_(n) _(8×1) . Further, the UE 704 mixes y_(1,n) _(2×1)with RF carriers of f₁ to generate 2 RF signals and transmits the RFsignals to the repeater 706-1 in slot 910-0 through the channel 1010which can be represented as H_(1,n) _(2×2) ⁽¹⁾.

The repeater 706-1 receives, in the slot 920-0, the RF signalstransmitted from the UE 704. The impact, of the rate conversion andfrequency translation (RCFT) process, to the base band signals can berepresented as T₁. The repeater 706-1 further transmits the RF signalsof f₂, generated through the RCFT process, to the base station 702 inthe slot 930-0 through the channel 1030 which can be represented asH_(1,n) _(8×2) . Accordingly, on the subcarrier n, the baseband signalsreceived by the base station 702 from the repeater 706-1 can berepresented as

r _(1,n) _(8×1) =H _(1,n) _(8×2) ⁽²⁾ ·T ₁ ·H _(1,n) _(2×2) ⁽¹⁾ ·P _(1,n)_(2×8) ·x _(n) _(8×1) +n ₁ =H _(1,n) _(8×2) ⁽²⁾ ·T ₁ ·H _(1,n) _(2×2)⁽¹⁾ ·y _(1,n) _(2×1) n ₁

n₁ is equivalent noise vector at the base station 702 which may containthe noise received at the repeater 706-1 and the base station 702.

Similarly, the repeaters 706-2, 706-3, 706-4 receive y_(2,n) _(2×1) ,y_(3,n) _(2×1) , y_(4,n) _(2×1) transmitted from the UE 704 on f₁ in theslots 920-1, 920-2, 920-3, respectively. The repeaters 706-2, 706-3,706-4 process the received RF signals through the RCFT processes andtransmit the result RF signals on f₂ in the slot 930-0.

The base station 702 receives the RF signals on f₂ transmitted from therepeaters 706-1 . . . 706-4 in the slot 940-0. The received basebandsignal r_(n) _(8×1) at the base station 702 can be expressed as the sumof all signals received from the repeaters 706-1, . . . , 706-4 asfollows:

$r_{n_{8 \times 1}} = {{r_{1,n_{8 \times 1}} + r_{2,n_{8 \times 1}} + r_{3,n_{8 \times 1}} + r_{4,n_{8 \times 1}}} = {{{H_{1,n_{8 \times 2}}^{(2)} \cdot T_{1} \cdot H_{1,n_{2 \times 2}}^{(1)} \cdot P_{1,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} + n_{1} + {H_{2,n_{8 \times 2}}^{(2)} \cdot T_{2} \cdot H_{2,n_{2 \times 2}}^{(1)} \cdot P_{2,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} + n_{2} + {H_{3,n_{8 \times 2}}^{(2)} \cdot T_{3} \cdot H_{3,n_{2 \times 2}}^{(1)} \cdot P_{3,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} + n_{3} + {H_{4,n_{8 \times 2}}^{(2)} \cdot T_{4} \cdot H_{4,n_{2 \times 2}}^{(1)} \cdot P_{4,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} + n_{4}} = {{{\lbrack {{H_{1,n_{8 \times 2}}^{(2)} \cdot T_{1} \cdot H_{1,n_{2 \times 2}}^{(1)}}\ldots{H_{4,n_{8 \times 2}}^{(2)} \cdot T_{4} \cdot H_{4,n_{2 \times 2}}^{(1)}}} \rbrack \cdot \begin{bmatrix}{P_{1,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} \\{P_{2,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} \\{P_{3,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}} \\{P_{4,n_{2 \times 8}} \cdot x_{n_{8 \times 1}}}\end{bmatrix}} + n} = {{{\lbrack {{H_{1,n_{8 \times 2}}^{(2)} \cdot T_{1} \cdot H_{1,n_{2 \times 2}}^{(1)}}\ldots{H_{4,n_{8 \times 2}}^{(2)} \cdot T_{4} \cdot H_{4,n_{2 \times 2}}^{(1)}}} \rbrack.\ \begin{bmatrix}y_{1,n_{2 \times 1}} \\y_{2,n_{2 \times 1}} \\y_{3,n_{2 \times 1}} \\y_{4,n_{2 \times 1}}\end{bmatrix}} + n} = {{H_{{eq},n} \cdot y_{n_{8 \times 1}}} + n}}}}}$

where the 8-rank matrix

H _(eq,n) =[H _(1,n) _(8×2) ⁽²⁾ ·T ₁ ·H _(1,n) _(2×2) ⁽¹⁾ . . . H _(4,n)_(8×2) ⁽²⁾ T ₄ ·H _(4,n) _(2×2) ⁽¹⁾].

As such, based on the equation r_(n) _(8×1) =H_(eq,n)·y_(n) _(8×1) +nand y_(i,n) _(2×8) =P_(i,n) _(2×8) ·x_(n) _(8×1) for i= 1, . . . , 4,the base station 702 can determine 8 layers baseband data signalsx_(1,n),x_(2,n), . . . ,x_(8,n).

Generally, the UE 704 has N_(T) transmission antennas, the base station702 has N_(R) reception antennas and the L repeaters 706-1, , 706-L withM_(T) transmission antennas and M_(R) reception antennas whereM_(T)=M_(R)=M are located between the UE 704 and the base station 702.The UE 704 may generate R layers baseband data signals. The receivedbaseband signal r_(n)∈

^(N) ^(R) ^(×1) at the n-th subcarrier at the base station 702 is thesum of signal transmitted from L repeaters 706-1, . . . , 706-L and itcan be expressed as below Equation (B):

$r_{n} = {{{{\sum}_{l = 1}^{L}H_{l,n}^{(2)}T_{l,n}{H_{l,n}^{(1)} \cdot P_{1,n} \cdot x_{n}}} + n_{n}} = {{{\sum}_{l = 1}^{L}H_{l,n}^{(2)}T_{l,n}{H_{l,n}^{(l)} \cdot \begin{bmatrix}y_{l,1,n} \\\ldots \\y_{l,N_{T},n}\end{bmatrix}}} + n_{n}}}$

where H_(l,n) ⁽²⁾∈

^(N) ^(R) ^(×M) denotes the channel matrix in the second hop from thel-th reapeater 706-1 to the base station 702, H_(l,n) ⁽¹⁾∈

^(M×N) ^(T) denotes the channel matrix in the first hop from the UE 704to the l-th repeater 706-1, T_(l,n)∈

^(M×M) is an amplifying matrix describing the mapping from the repeaterinput to the repeater output, P_(l,n)∈

^(N) ^(T) ^(×R) represents the precoding matrix for the l-th spatialtransmitting setting, and n_(n)∈

^(N) ^(R) ^(×1) is the equivalent noise vector at the base station 702which may contain the noise received at the repeaters 706-1, . . . ,706-L and the base station 702. In a period of L TTI₁ intervals, the UE704 may be considered as having L·N_(T) effective antennas. In thisformulation, the rank-R signal x_(n) is precoded by P_(l,n) andtransmitted by the UE over the l-th TTI₁ interval between(t₀×TTI₂+(l−1)×TT₁t₀×TTI₂+l×TTI₁) for l=1, . . . ,L . By stacking theprecoding matrix over L TTI₁ intervals, we can formulate the equivalentprecoding matrix as P_(eq,n)=[P_(i,n) ^(T), . . . ,P_(L,n) ^(T)]^(T)∈

^(LN) ^(T) ^(×R) and the received baseband signal r_(n)∈

^(N) ^(R) ^(×1) can be rewrite as

$r_{n} = {{{\lbrack {{H_{1,n}^{(2)} \cdot T_{1,n} \cdot H_{1,n}^{(1)}}\ldots{H_{L,n}^{(2)} \cdot T_{L,n} \cdot H_{L,n}^{(1)}}} \rbrack_{N_{R} \times {LN}_{T}} \cdot \begin{pmatrix}P_{1,n} \\\ldots \\R_{L,n}\end{pmatrix} \cdot x_{n}} + n_{n}} = {{H_{{eq},n} \cdot P_{{eq},n} \cdot x_{n}} + n_{n}}}$

where H_(eq,n)=[H_(1,n) ⁽²⁾·T_(1,n)·H_(1,n) ⁽¹⁾ . . . H_(L,n)⁽²⁾T_(L,n)·H_(L,n) ⁽¹⁾]∈

^(N) ^(R) ^(×LN) ^(T) is the equivalent channel matrix. The j-th layerdata corresponding to the j-th element of x_(n) is precoded by the j-thcolumn of P_(eq,n). Note each 8-by-1 precoder (i.e., each column vectorof P_(eq,n)) used for each layer can be expressed by four 2-by-1precoders separately used in the 4 TTIs.

In both NCJT and CJT approaches above, the precoders used by UE aredetermined either by base station or by the UE itself, according tochannel state information of UL channels. The base station can determinethe precoders based on measuring sounding reference signal sent by theUE to obtain channel state information and can indicate the precoders tothe UE for UL data transmissions. For the case where the UE determinesthe precoders, the UE may rely on measuring reference signals sent fromthe base station and may assume channel reciprocity to obtain channelstate information.

FIG. 12 is a diagram 1200 illustrating signal transformation at arepeater. Using the reception antenna 722-1 of the repeater 706-1 as anexample, the FFT component 751 of the reception antenna 722-1 has a sizeN₁. The filtered digital samples from the conversion component 754 arepassed through a down-sampling block, when necessary, to convert thedata rate of the digital sample stream to match the FFT size N₁.Accordingly, the positions of the OFDM symbols can be determined in thedown converted digital samples. Once digital samples within an OFDMsymbol are found, the CP removal component 753 removes the cyclic prefix(CP) used to prevent inter-symbol interference (ISI). The serial toparallel component 752 groups N₁ data samples as an input vector for theFFT component 751. The FFT component 751 outputs N₁ modulation symbols{tilde over (g)}_(k,1) 1220, which are a combination of s_(k,1) tos_(k,2) as received at the reception antenna 722-1 of the repeater706-1. Further, the N₁ modulation symbols {tilde over (g)}_(k,1) 1220are carried on N₁ subcarriers 1210 with a SCS₁.

As described supra, each of the repeaters 706-1 . . . 706-K hastransmission antennas 724-1, 724-2 and uses a respective transmissionchain 760 to generate RF signals to be transmitted through eachtransmission antenna. Further, each transmission chain 760 correspondsto a respective reception chain 750. As described infra, modulationsymbols received through a reception antenna of the repeater areretransmitted through a corresponding transmission antenna.

Using the repeater 706-1 as an example (M_(r)=M_(t)=M=2), the receptionantennas 722-1, 722-2 correspond to the transmission antennas 724-1,724-2. More specifically, {tilde over (g)}_(k,1) 1220 received throughthe reception chain 750 of the reception antenna 722-1 are retransmittedthrough the transmission chain 760 of the transmission antenna 724-1. Ina more general case with M_(r)≠M_(t), a mapping from the M_(t)transmission antennas to the M_(r) reception antennas is needed and maybe provided by a linear transformation matrix. If M_(r) is equal toM_(t), the linear transformation matrix can be simply an identity matrixrepresenting one-to-one mapping between one reception antenna and onetransmission antenna. N₂ modulation symbols m_(k,1) 1240, which areinputs for retransmitting through the transmission chain 760 of thetransmission antenna 724-1 are selected from elements in {tilde over(g)}_(k,1) received in the reception antenna 722-1, or are linearcombination of the elements in {tilde over (g)}_(k,1).

The transmission chain 760 uses N₂ subcarriers 1230 having a SCS₂. TheIFFT component 761 uses N₂ points and has N₂ inputs/outputs. Therepeater 706-1 is configured with a predetermined rule that maps the N₁outputs of the FFT component 751 to the N₂ inputs of the IFFT component761.

More specifically, the repeater 706-1 applies a group of N₂ modulationsymbols m_(k,1) 1240 to the N₂ subcarriers 1230 in an OFDM symbol B. TheN₂ subcarriers 1230 carrying the N₂ modulation symbols m_(k,1) 1240 aresent to the IFFT component 761 with N₂ inputs. The N₂ digital samplesoutput from the IFFT component 761 are treated as a time sequence andsent to the parallel to serial component 762 to form a time domainsignal. The CP insertion component 763 receives the time domain signaland adds a cyclic prefix, resulting a time domain signal spanning anOFDM symbol B, which corresponds to SCS₂. The resulting time domainsignal is in digital form, and is processed through a conversioncomponent 764 that includes a rate converter and/or filter(s) to achievea desired sample rate. The converted time domain signal in digital formis sent to the digital-to-analog converter 765, which accordinglygenerates an analog time domain signal. Subsequently, the up converter766 receives the analog time domain signal and mixes the analog timedomain signal with a second carrier frequency (f₂) to generate a RFsignal. The RF signal is transmitted through the transmission antenna724-1 of the repeater 706-1. In particular, the second carrier frequencyof the RF signals transmitted from the repeaters 706-1 . . . 706-K maybe in FR1.

Referring back to FIG. 7 , in certain configurations, modulation symbolsto be transmitted through an i^(th) antenna port (e.g., the 1^(st)antenna port corresponding to the antenna 712-1) of the UE 704 in ak^(th) OFDM symbol A are denoted as z_(k,i), with z_(k,i)∈

^(N) ² ^(×1). z_(k,i) are mapped to the selected N₂ (e.g., 1024) inputsout of total N₁ inputs (e.g., 4096) , denoted as z_(k,i)∈

^(N) ² ^(×1), of the IFFT component 741 according to an invertiblemapping function f(i), where z_(k,i)=[z_(k,i,0),z_(k,i,1), . . .,z_(k,i,N) ₂ ⁻¹]^(T) and {tilde over (z)}_(k,i)=[{tilde over(z)}_(k,i,0),{tilde over (z)}_(k,i,1), . . . ,{tilde over (z)}_(k,i,N) ₂⁻¹]^(T). f(i) returns the index in {tilde over (z)}_(k,i) that is mappedfrom the i^(th) element in z_(k,i). That is, the function f(i) gives theindex in the transformed vector {tilde over (z)}_(k,i) that correspondsto the i^(th) element in the original vector z_(k,i). As an example, thefunction can be defined as

${{f(i)} = {i + \frac{N_{1} - N_{2}}{2}}}.$

Accordingly, it can be determined that

${{\overset{˜}{z}}_{k,i} = \begin{bmatrix}0_{\frac{N_{1} - N_{2}}{2}}^{T} & z_{k,i}^{T} & 0_{\frac{N_{1} - N_{2}}{2}}^{T}\end{bmatrix}^{T}},$

where

$0_{\frac{N_{1} - N_{2}}{2}}^{T}$

is a row vector of zeros with the length

$\frac{N_{1} - N_{2}}{2}.$

The N₂ modulation symbols in z_(k,i) are created by layer mapping andprecoding stages in the UE 704 based on encoded data streams. Followingthe invertible mapping function f(i), the resulting N₁ modulationsymbols in {tilde over (z)}_(k,i) are fed into the IFFT component 741 ofthe transmission chain 740 for the i^(th) antenna port. The IFFTcomponent 741 performs the inverse fast Fourier transform on the inputvector to generate a time-domain signal with N₁ samples. After the IFFToperation, the parallel to serial component 742 processes the N₁time-domain samples and outputs a single time-domain signal. The CPinsertion component 743 adds a cyclic prefix to this time-domain signal,resulting in an OFDM symbol A with a subcarrier spacing of SCS₁. Theoutput signal from the CP insertion component 743 is then sent to theconversion component 744, which performs rate conversion and filteringto adapt the signal for transmission. The digital-to-analog converter745 subsequently converts the processed digital signal into an analogsignal, which is then mixed with the first carrier frequency f₁ by theup converter 746. The mixed signal is then transmitted through thetransmission antenna corresponding to the i^(th) antenna port (e.g., theantenna 712-1 or 712-2) of the UE 704.

As described supra, the repeaters 706-1 . . . 706-K receives the RFsignals from the UE 704 and processes the received RF signals. Inparticular, as described supra, the inverse function

${f^{- 1}(i)} = {i - \frac{N_{1} - N_{2}}{2}}$

is utlized to map {tilde over (g)}_(k,i) to m_(k,i) at the repeaters706-1 . . . 706-K. As a result, the input vector m_(k,i) of the IFFTcomponent 761 can be expressed as

$\begin{bmatrix}0_{\frac{N_{1} - N_{2}}{2}}^{T} & {\overset{\sim}{g}}_{k,i}^{T} & 0_{\frac{N_{1} - N_{2}}{2}}^{T}\end{bmatrix}^{T}$

at the repeaters 706-1 . . . 706-K.

Accordingly, the repeaters 706-1 . . . 706-K can use an option describedinfra to construct m_(k,i), which are the input vector of the IFFTcomponent 761, based on {tilde over (g)}_(k,i). The mapping from {tildeover (g)}_(k,i)=. . . ,[{tilde over (g)}_(k,i,0), . . . ,{tilde over(g)}_(k,i,N) ₁ ⁻¹]^(T) to make m_(k,i)=[m_(k,i,0), . . . ,m_(k,i,N) ₂⁻¹]^(T) is determined according to a rule that maps z_(k,i)=[z_(k,i,0),. . . ,z_(k,i,N) ₂ ⁻¹]^(T) to {tilde over (z)}_(k,i)=[{tilde over(z)}_(k,i,0), . . . ,{tilde over (z)}_(k,i,N) ₁ ⁻¹]^(T) in atransmission (Tx) chain of the UE 704. m_(k,i)∈

^(N) ² ^(×1) are the inputs of the IFFT function in the Tx-chain of therepeater 706-1, z_(k,i)∈

^(N) ² ^(×1) carry the baseband signal in the frequency domain for theTx antenna port directed to the Tx-chain of the UE 704, and {tilde over(z)}_(k,i) ∈

^(N) ² ^(×1) are the inputs of the IFFT at the UE 704. N₂ elements of{tilde over (z)}_(k,i) are one-to-one mapped from all the elements inz_(k,i). An invertible mapping, denoted as f(i) returns the index in{tilde over (z)}_(k,i) that is mapped from the i-th element in z_(k,i).For the other elements not in the range of f(·), one option is to setthem to zeros. Then the mapping from {tilde over (g)}_(k,i) to m_(k,i)is done by the inverse function f⁻¹(·) that takes the elements whoseindexes are in the range of f(·). For example, given the invertiblefunction

${{f(i)} = {i + \frac{N_{1} - N_{2}}{2}}},$

we have {tilde over (z)}_(k,i)=[0_((N) ₁ _(−N) ₂ _()/2)z_(k,i)^(T)0_((N) ₂ _(−N) ₁ _()/2)]^(T) where 0_((N) ₂ _(−N) ₁ _()/2) is a zerovector of size (N₂−N₁)/2. Then m_(k,i) is taken from the center N₂elements of {tilde over (g)}_(k,i). Finally, IFFT component 761 isobtained from m_(k,i) through the N₂ -point FFT function and then theP-to-S conversion in the Tx chain.

FIG. 13 is a diagram 1300 illustrating signal reception at the basestation 702. In general, the base station 702 have N R reception antennaports. In this example, each reception antenna corresponding to areception antenna. (That is, there are N_(R) antennas.) In otherexamples, each reception antenna port may be associated with one ormultiple physical antennas, and may be referred to as a beamformedantenna port. In this example, the base station 702 has receptionantennas 710-1, 710-2, . . . 710-8 corresponding to antenna ports 1350-1to 1350-8.

RF signals received at each reception antenna of the base station 702are processed through a respective reception chain 790. Similar to areception chain 750 of a repeater, the reception chain 790 includes anFFT component 791, a serial to parallel component 792, a CP removalcomponent 793, filter(s) 794, an analog-to-digital converter 795, and adown converter 796.

More specifically, the base station 702 receives the RF signals from therepeaters 706-1 . . . 706-K and extracts, from the RF signals, basebandsignals r_(n) carried on the n^(th) subcarrier of the N₂ subcarriers1330. r_(n) is a vector [s_(1,n), . . . , s_(8,n)]^(T), where s_(i,n) isthe baseband signal received at the i^(th) reception antenna of the basestation 702 corresponding to the n^(th) subcarrier. For the i^(th)reception antenna, the received RF signal is first mixed down tobaseband with the down converter 796 and converted to digital samples bythe analog-to-digital converter 795. The digital samples are filteredusing one or more filters 794 to remove out-of-band interference. The CPremoval component 793 removes the cyclic prefix before the serial toparallel component 792 groups the filtered digital samples into N₂samples per OFDM symbol. The FFT component 791 then performs an N₂-point FFT on these samples to obtain the N₂ modulation symbolss_(i)=[s_(i,1), . . . ,s_(i,n), . . . , s_(i,N) ₂ ]^(T) at the i^(th)reception antenna corresponding to the N₂ subcarriers.

Next, the base station 702 performs signal processing to determine thetransmitted baseband data signals x based on the received basebandsignals r_(n) and the knowledge of the system configuration, includingthe mappings from z_(k,i) to {tilde over (z)}_(k,i), and from {tildeover (g)}_(k,i) to m_(k,i). The base station 702 takes into account themapping rules and the channel estimation information from both the firstand second frequencies in its signal processing. The signal processingtypically involves decoding signals transmitted via all the RCFTrepeaters and the UE 704. In particular, the base station 702 canutilize the mapping provided by the f(i) function to reconstruct theoriginal signals transmitted by the UE 704. This allows the base station702 to accurately decode the transmitted information and makeappropriate decisions based on the recovered data.

-   -   The base station 702 performs channel estimation procedures to        extract channel state information (CSI) related to the links        between the UE 704 and itself This CSI is useful for determining        how to process and decode the received signals optimally. The        base station 702 may estimate an equivalent channel response        that is formed by precoders used by the UE and a channel between        the reception antennas at the base station and the effective        antennas at the UE. Further, based on the CSI, the base station        702 may estimate H_(eq,n) described supra, which can be        considered as the equivalent channel matrix of the overall        system for the n -th subcarrier. This equivalent channel matrix        H_(eq,n) considers the effects of all transmissions, multipath        fading, and beamforming/precoding techniques employed by the UE        704 and base station 702.

As such, based on r_(n), H_(eq,n), and P_(eq,n) with respect to theEquation (A) or (B) described supra, the base station 702 can usevarious multi-antenna signal processing techniques to estimate anddecode the transmitted data symbols x_(n) from the UE 704. When usingthe RCFT repeaters-assisted uplink MIMO system, some system parametersand control information need to be shared among the UE 704, the basestation (BS) 702, and the RCFT repeaters 706-1, . . . , 706-K. Thisinformation sharing ensures proper system operation and enables the BS702 to recover the information transmitted by the UE 704.

The UE 704 needs to receive the following information from the BS 702:(a) available time-frequency resources in the second frequency for UE'stransmission; (b) the mapping from z_(k,i) to {tilde over (z)}_(k,i);and/or (c) the TCI-state or spatial relation for the Tx beam (Tx spatialfiltering) used in each TTI₁ interval.

In addition, the BS 702 needs to provide the RCFT repeaters 706-1, . . ., 706-K with necessary information to receive the UE's transmission inthe first frequency and forward the signal in the second frequency. Thisinformation may include: (a) frequency band parameters (carrierfrequencies) for the first frequency and the second frequency; (b) theassociated channel bandwidths (B₁, B₂) and subcarrier spacings (SCS₁,SCS₂) in the first frequency and in the second frequency; (c) theTCI-state or spatial relation for Rx beam (Rx spatial filtering) used ineach TTI1 interval; and/or (d) the FFT and IFFT sizes (N₁, N₂), and themapping from {tilde over (g)}_(k,i) to m_(k,i). The necessaryinformation may be directly signaled to the RCFT repeaters, or may besignaled to the UE first and then forwarded to the RCFT repeaters by theUE.

By providing this information to the UE and the RCFT repeaters, thesystem ensures efficient data transmission and reception, which canfurther improve the uplink communication between the UE and the basestation.

FIG. 14 is a diagram 1400 illustrating a method (process) for uplinkcommunications. The method may be performed by a UE. At operation 1402,the UE measures reference signals transmitted from a base station todetermine channel state information for determining the R precoders. Atoperation 1406, the UE receives indications of R precoders from the basestation.

At operation 1408, the UE receives additional control information fromthe base station, which may include available time-frequency resourcesfor UE transmission and a transmission control information state orspatial relation for a transmission beam used in each of the L firsttransmission time intervals.

At operation 1410, the UE receives control information from a basestation. This control information includes parameters for one or morerepeaters to receive the UE's transmission in a first frequency andforward the signal in a second frequency. The control information mayalso include frequency band parameters for the first and secondfrequencies, associated channel bandwidths and subcarrier spacings inthe first and second frequencies, a transmission control informationstate or spatial relation for a reception beam used in each firsttransmission time interval, and fast Fourier transform (FFT) and inverseFFT sizes, as well as a mapping relationship from data signals on the N₁subcarriers in the first frequency to data signals on the N₂ subcarriersin the second frequency. At operation 1412, the UE forwards the controlinformation, including parameters, to the one or more repeaters.

At operation 1414, the UE generates R layers of baseband data signals tobe carried on N₂ subcarriers, where N₂ and R are positive integers. Atoperation 1416, the UE maps each of the R layers of baseband datasignals to N_(T) antennas of the UE in some or all of L firsttransmission time intervals by R precoders, respectively. Here, N_(T)and L are positive integers, and each of the R precoders includesL·N_(T) elements.

Finally, at operation 1418, the UE transmits a first OFDM-basedtime-domain signal corresponding to the mapped baseband data signalsacross the L first transmission time intervals to a base station via oneor more repeaters. The L first transmission time intervals correspond toone second transmission time interval.

In some embodiments, N_(T) is less than R. The first OFDM-basedtime-domain signal may be generated according to a first subcarrierspacing and N₁ subcarriers, where N₁ is a positive integer. Eachmodulation symbol carried by each subcarrier of the N₂ subcarriers maybe mapped from a linear combination of modulation symbols on one or moresubcarriers of the N₁ subcarriers. The mapping function can be definedas

${j = {i + \frac{N_{1} - N_{2}}{2}}},$

such that the modulation symbol carried by an i-th subcarrier of the N₂subcarriers is mapped from a j-th subcarrier of the N₁ subcarriers. Thetime-domain signal is sent to the one or more repeaters that transformthe first OFDM-based time-domain signal to a second OFDM-basedtime-domain signal corresponding to N₂ subcarriers and a secondsubcarrier spacing.

The sequence of the operations detailed supra is provided as an exampleand should not be considered as restrictive. These operations may bereorganized based on different configurations.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination therof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication of a userequipment (UE), comprising: generating R layers of baseband data signalsto be carried on N₂ subcarriers, N₂ and R being positive integers;mapping each of the R layers of baseband data signals to N_(T) antennasof the UE in some or all of L first transmission time intervals by Rprecoders, respectively, wherein N_(T) and L are positive integers andeach of the R precoders includes L·N_(T) elements; and transmitting, toa base station via one or more repeaters, a first OFDM-based time-domainsignal corresponding to the mapped baseband data signals across the Lfirst transmission time intervals, wherein the L first transmission timeintervals correspond to one second transmission time interval.
 2. Themethod of claim 1, wherein N_(T) is less than R.
 3. The method of claim1, wherein the first OFDM-based time-domain signal is generatedaccording to a first subcarrier spacing and N₁ subcarriers, N₁ being apositive integer.
 4. The method of claim 3, wherein each modulationsymbol carried by each subcarrier of the N₂ subcarriers is mapped from alinear combination of modulation symbols on one or more subcarriers ofthe N₁ subcarriers.
 5. The method of claim 4, wherein the mappingfunction is defined as ${j = {i + \frac{N_{1} - N_{2}}{2}}},$ such thatthe modulation symbol carried by an i-th subcarrier of the N₂subcarriers is mapped from a j-th subcarrier of the N₁ subcarriers. 6.The method of claim 4, wherein the time-domain signal is sent to arepeater that transforms the first OFDM-based time-domain signal to asecond OFDM-based time-domain signal corresponding to N₂ subcarriers anda second subcarrier spacing.
 7. The method of claim 1, furthercomprising: receiving indications of the R precoders from the basestation.
 8. The method of claim 1, further comprising: measuringreference signals transmitted from the base station to determine channelstate information for determining the R precoders.
 9. The method ofclaim 1, further comprising: receiving control information from a basestation, the control information including at least one of: (a)available time-frequency resources for UE transmission, and (b) atransmission control information state or spatial relation for atransmission beam used in each of the L first transmission timeintervals.
 10. The method of claim 1, wherein the UE is configured totransmit baseband data signals through one or more repeaters, andwherein the method further comprises: receiving control information froma base station, the control information including parameters for the oneor more repeaters to receive transmission of the UE in a first frequencyand forward the signal in a second frequency.
 11. The method of claim10, further comprising: forwarding, to the one or more repeaters, thecontrol information including parameters.
 12. The method of claim 10,wherein the control information includes at least one of: (a) frequencyband parameters for the first and second frequencies, (b) associatedchannel bandwidths and subcarrier spacings in the first and secondfrequencies, (c) a transmission control information state or spatialrelation for a reception beam used in each first transmission timeinterval, and (d) fast Fourier transform (FFT) and inverse FFT sizes,and a mapping relationship from data signals on the N₁ subcarriers inthe first frequency to data signals on the N₂ subcarriers in the secondfrequency.
 13. An apparatus for wireless communication, the apparatusbeing a user equipment (UE), comprising: a memory; and at least oneprocessor coupled to the memory and configured to: generate R layers ofbaseband data signals to be carried on N₂ subcarriers, N₂ and R beingpositive integers; map each of the R layers of baseband data signals toN_(T) antennas of the UE in some or all of L first transmission timeintervals by R precoders, respectively, wherein N_(T) and L are positiveintegers and each of the R precoders includes L·N_(T) elements; andtransmit, to a base station via one or more repeaters, a firstOFDM-based time-domain signal corresponding to the mapped baseband datasignals across the L first transmission time intervals, wherein the Lfirst transmission time intervals correspond to one second transmissiontime interval.
 14. The apparatus of claim 13, wherein N_(T) is less thanR.
 15. The apparatus of claim 13, wherein the at least one processor isfurther configured to generate the first OFDM-based time-domain signalaccording to a first subcarrier spacing and N₁ subcarriers, N₁ being apositive integer.
 16. The apparatus of claim 15, wherein the at leastone processor is further configured to map each modulation symbolcarried by each subcarrier of the N₂ subcarriers from a linearcombination of modulation symbols on one or more subcarriers of the N₁subcarriers.
 17. The apparatus of claim 16, wherein the mapping functionis defined as ${j = {i + \frac{N_{1} - N_{2}}{2}}},$ such that themodulation symbol carried by an i-th subcarrier of the N₂ subcarriers ismapped from a j-th subcarrier of the N₁ subcarriers.
 18. The apparatusof claim 16, wherein the at least one processor is further configured tosend the time-domain signal to a repeater that transforms the firstOFDM-based time-domain signal to a second OFDM-based time-domain signalcorresponding to N₂ subcarriers and a second subcarrier spacing.
 19. Theapparatus of claim 13, wherein the at least one processor is furtherconfigured to: receive indications of the R precoders from the basestation.
 20. A computer-readable medium storing computer executable codefor wireless communication of a user equipment (UE), comprising code to:generate R layers of baseband data signals to be carried on N₂subcarriers, N₂ and R being positive integers; map each of the R layersof baseband data signals to N_(T) antennas of the UE in some or all of Lfirst transmission time intervals by R precoders, respectively, whereinN_(T) and L are positive integers and each of the R precoders includesL·N_(T) elements; and transmit, to a base station via one or morerepeaters, a first OFDM-based time-domain signal corresponding to themapped baseband data signals across the L first transmission timeintervals, wherein the L first transmission time intervals correspond toone second transmission time interval.